1. Field of the Invention
This invention relates generally to electric drive systems and, more particularly, to a combination of a cranking inverter and a boost converter in a series hybrid drive system.
2. Description of the Related Art
Heat engine driven alternators for series hybrid vehicle drives produce significant emissions during cold and warm start-up using conventional dc cranking (starter) motors and normal engine controls.
As disclosed in commonly assigned King, U.S. Pat. No. 5,345,154, issued Sep. 6, 1994, which is herein incorporated by reference, a field-controlled multi-phase alternator coupled to a full bridge rectifier are useful as a series hybrid propulsion drive for a vehicle. During high power operations, including vehicle accelerations and while climbing grades, for example, the heat engine speed is necessarily high and the uncontrolled full bridge rectifier efficiently converts the high power alternator output signal from ac to dc. However, field-controlled multi-phase alternators typically do not have sufficient voltage control to permit battery charging at low to medium power levels while operating at low heat engine speeds and still minimize emissions and maximize fuel economy. In these systems, alternator field control limitations often require the heat engine to operate at higher speeds than is necessary to supply the desired power, and thus heat engine emissions and fuel economy are compromised during low to medium power level battery charging.